A psychiatric hospital (also called at various places and times, mental hospital, mental ward, asylum or sanitarium), is a hospital specializing in the treatment of persons with mental illness. Psychiatric wards differ only in that they are a unit of a larger hospital.

The history of psychiatric hospitals is linked heavily with social and scientific attitudes towards mentally ill people, which have changed greatly over the past centuries.

Generally these are open units that are less secure than crisis stabilization units. They are not used for acutely suicidal persons; the focus in these units is to make life as normal as possible for patients while continuing treatment to the point where they can be discharged. However, patients are usually still not allowed to hold their own medications in their rooms, because of the risk of an impulsive overdose. While some open units are still physically unlocked, other open units still use locked entrances and exits. This is to keep patients from escaping, which may be described as "leaving impulsively," or leaving without being discharged from the unit.

Another type of psychiatric hospital is a medium term, which provides care lasting several weeks. Most drugs used for psychiatric purposes take several weeks to take effect, and the main purpose of these hospitals is to watch over the patient while the drugs begin their expected effect and the patient can be discharged.

In the UK, at least, long-term care facilities are now being replaced with smaller secure units (some within the hospitals listed above). Modern buildings, modern security and being locally sited to help with reintegration into society once medication has stabilized the condition are often features of such units. An example of this is the Three Bridges Unit, in the grounds of Hanwell Asylum in West London. However these modern units have the goal of treatment and rehabilitation back into society within a short time-frame (two or three years) and not all forensicpatients' treatment can meet this criterion, so the large hospitals mentioned above often retain this role.

One final type of institution for the mentally ill, that is not a hospital, is a community-based halfway house. These houses provide assisted living for patients with mental illnesses for an extended period of time. These institutions are considered to be one of the most important parts of a mental health system by many psychiatrists, although some localities fail to provide sufficient funding for them, such provision being seen as costly.

In some countries the mental institution may be used for the incarceration of political prisoners, as a form of punishment (see Psikhushka). In the United States, more so in the past than now (although it still happens) a 72 hour hold would be placed on a person by police when that person had committed no crime, but the police still wanted to take action against that person.

Some anti-psychiatry activists have advocated for the abolition of long-term hospitals for the criminally insane, including on the grounds that those judged not guilty by reason of insanity should not then be indefinitely confined with potentially less legal rights, or on the converse grounds that insanity is not a coherent concept and so should not be a basis for different treatment.